Pesticide compositions, for example, herbicide compositions containing N-(phosphonomethyl)glycine (“glyphosate”), are typically applied to target plants by spraying. A portion of the spray droplets are typically very small, for example, less than about 200 microns, which are subject to off-target movement, termed “drift”. Drift is undesirable because it reduces the amount of active herbicide applied to the target plant and risks unintended application of the active herbicide to non-target plants.
Common approaches to reducing drift are to add a thickening agent, for example, polysaccharides, polyacrylamides, to the herbicide composition, and/or to control process variables, such as by reducing spray pressure, or to using a spray nozzle, for example, an air induction spray nozzle, that is designed to reduce drift (note, however, that thickeners are typically not used in combination with air induction nozzles).
In addition, a wide variety of adjuvants, including adjuvant compositions that containing alkylated seed oils and emulsifiers, are generally known for use in modifying the properties, such as efficacy against target pests, of agricultural pesticide formulations, including glyphosate herbicide compositions, see, e.g., Miller, D. K., et. al., “Johnsongrass (Sorgum halepense) Control and Rainfastness with Glyphosate and Adjuvants”, Weed Technology, 1998, Vol. 12:617-622, and U.S. Pat. No. 6,432,884 B1. In this example the adjuvant mainly consists of a silicone surfactant as well as alkylated seed oil and nonionic surfactants. Silicone based surfactants are known to be unstable in acidic and basic conditions. Generally the optimum pH for these surfactants is in the range of 6 to 8 (Murphy et al., Proc Brighton Crop Prot Conf-Weeds 1991). Among other disadvantages of silicone surfactants are the incompatibility with non-silicone adjuvants, reduced activity of herbicides due to spray run-offs or quick evaporation. On the other hand, some authoritative sources have discouraged use of oil adjuvants with glyphosates, e.g., North Dakota State University's 2004 North Dakota Weed control Guide states, at pg 71, that “glyphosate should never be used with oil adjuvants because glyphosate is very water soluble (water+oil do not mix)”.
There remains a continuing interest in efficient spray application of pesticide compositions, particularly glyphosate compositions, to target plants with minimal drift, while maintaining high efficacy against such target plants.